Problem: The sum of an infinite geometric series is $27$ times the series that results if the first three terms of the original series are removed. What is the value of the series' common ratio?
Let's denote the first term as $a$ and the common ratio as $r.$ Additionally, call the original sum of the series $S.$ It follows that \[\frac{a}{1-r}=S.\] After the first three terms of the sequence are removed, the new leading term is $ar^3.$ Then one $27^{\text{th}}$ of the original series is equivalent to \[\frac{ar^3}{1-r}=r^3\left( \frac{a}{1-r}\right)=\frac{S}{27}.\]

Dividing the second equation by the first, $r^3= \frac{1}{27}$ and $r=\boxed{\frac{1}{3}}.$